Journal of Bacteriology, April 1999, p. 2067-2074, Vol. 181, No. 7
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Department of Microbiology and Immunology, Emory University School of Medicine, 3001 Rollins Research Center, Atlanta, Georgia 30322
Received 30 October 1998/Accepted 23 January 1999
Neisseria meningitidis uses hemoglobin (Hb) as an iron
source via two TonB-dependent outer membrane receptors, HmbR and HpuB. Analysis of 25 epidemiologically unrelated clinical isolates from serogroups A, B, C, and Y revealed that 64% strains possessed both Hb
receptor genes. Examination of the hmbR expression pattern in strains in which the hpuB gene was genetically
inactivated revealed two distinct Hb utilization phenotypes.
Five strains retained the ability to grow as a confluent lawn, while
seven grew only as single colonies around Hb discs. The single-colony phenotype observed for some hpuB mutants is suggestive of
phase variation of hmbR. The length of the poly(G) tract
starting at position +1164 of hmbR absolutely correlated
with the two Hb utilization phenotypes. All five strains that grew as
confluent lawns around Hb discs possessed either 9 or 12 consecutive G
residues. All seven strains that grew as single colonies around Hb
discs had poly(G) tracts of a length other than 9 or 12. These
single-colony variants that arose around the Hb discs had poly(G)
tracts with either 9 or 12 consecutive G residues restoring the
hmbR reading frame. Inactivation of hmbR in
these strains resulted in a loss of Hb utilization, demonstrating that
the change in the hmbR gene was responsible for the
phenotypic switch. The switching rates from hmbR phase off
to phase on were ~5 × 10
4 in four
serogroup C strains, 2 × 10
2 in the serogroup A
isolate, and 7 × 10
6 in the serogroup B isolate.
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